584 Mr. De la Beche and Mr. Conybeare on 
runs into the annular suture in the 12th. Fig. 1 represents the 
earliest form ; fig. 2. the same, with the tubercular process attached, 
but from another skeleton; fig. 3. the 12th vertebra; fig. 4. 
the 13th. 
In the course of the succeeding four vertebra? the upper of the 
two notches runs into and extends the margin of the annular suture ; 
and in the next, (the 18th) the lower notch becomes a distinct 
tubercle ; thus two articulating surfaces are afforded, one on the 
tubercle, and a second on the cavity formed by the prolongation 
of the lip of the suture, of which the former must receive the head, 
and latter the tubercle of the anterior ribs. It will be remembered 
that a structure exactly similar was pointed out in the cervical 
and anterior dorsal vertebrae of the Ichthyosaurus; and it cor- 
responds also in some degree, at least, in the office of these parts, 
with the first dorsal vertebra of the Crocodile, in which the transverse 
process is not yet fully developed, and remains only a tubercle. 
Fig. 5 A, and fig. 5 B, represent the 18th vertebra in two points 
of view. 
At length the lower tubercle also disappears, and is swallowed 
up in a still longer prolongation of the margin of the annular 
suture ; at the same time the stems by which the annular part was 
attached to the body expand their bases laterally, so as to form in- 
cipient transverse processes : these at first point downwards, and 
are close to the middle of the side, but as they become longer they 
rapidly ascend and point upwards ; this character extends through 
the middle of the dorsal series ; thence they again begin to incline 
downwards in the posterior dorsals, and in the last, which bears a 
very short rib, become very much reduced. All the vertebra? from 
the first developement of the transverse process (27 in number) 
carry the ribs on a single articulating surface at the end . of that pro- 
